x86/lguest: Remove lguest support

Lguest seems to be rather unused these days. It has seen only patches
ensuring it still builds the last two years and its official state is
"Odd Fixes".

Remove it in order to be able to clean up the paravirt code.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: boris.ostrovsky@oracle.com
Cc: lguest@lists.ozlabs.org
Cc: rusty@rustcorp.com.au
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20170816173157.8633-3-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 1239 deletions

diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
deleted file mode 100644
index 0bc127e9f16a..000000000000
--- a/drivers/lguest/page_tables.c
+++ /dev/null
@@ -1,1239 +0,0 @@
-/*P:700
- * The pagetable code, on the other hand, still shows the scars of
- * previous encounters.  It's functional, and as neat as it can be in the
- * circumstances, but be wary, for these things are subtle and break easily.
- * The Guest provides a virtual to physical mapping, but we can neither trust
- * it nor use it: we verify and convert it here then point the CPU to the
- * converted Guest pages when running the Guest.
-:*/
-
-/* Copyright (C) Rusty Russell IBM Corporation 2013.
- * GPL v2 and any later version */
-#include <linux/mm.h>
-#include <linux/gfp.h>
-#include <linux/types.h>
-#include <linux/spinlock.h>
-#include <linux/random.h>
-#include <linux/percpu.h>
-#include <asm/tlbflush.h>
-#include <linux/uaccess.h>
-#include "lg.h"
-
-/*M:008
- * We hold reference to pages, which prevents them from being swapped.
- * It'd be nice to have a callback in the "struct mm_struct" when Linux wants
- * to swap out.  If we had this, and a shrinker callback to trim PTE pages, we
- * could probably consider launching Guests as non-root.
-:*/
-
-/*H:300
- * The Page Table Code
- *
- * We use two-level page tables for the Guest, or three-level with PAE.  If
- * you're not entirely comfortable with virtual addresses, physical addresses
- * and page tables then I recommend you review arch/x86/lguest/boot.c's "Page
- * Table Handling" (with diagrams!).
- *
- * The Guest keeps page tables, but we maintain the actual ones here: these are
- * called "shadow" page tables.  Which is a very Guest-centric name: these are
- * the real page tables the CPU uses, although we keep them up to date to
- * reflect the Guest's.  (See what I mean about weird naming?  Since when do
- * shadows reflect anything?)
- *
- * Anyway, this is the most complicated part of the Host code.  There are seven
- * parts to this:
- *  (i) Looking up a page table entry when the Guest faults,
- *  (ii) Making sure the Guest stack is mapped,
- *  (iii) Setting up a page table entry when the Guest tells us one has changed,
- *  (iv) Switching page tables,
- *  (v) Flushing (throwing away) page tables,
- *  (vi) Mapping the Switcher when the Guest is about to run,
- *  (vii) Setting up the page tables initially.
-:*/
-
-/*
- * The Switcher uses the complete top PTE page.  That's 1024 PTE entries (4MB)
- * or 512 PTE entries with PAE (2MB).
- */
-#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
-
-/*
- * For PAE we need the PMD index as well. We use the last 2MB, so we
- * will need the last pmd entry of the last pmd page.
- */
-#ifdef CONFIG_X86_PAE
-#define CHECK_GPGD_MASK		_PAGE_PRESENT
-#else
-#define CHECK_GPGD_MASK		_PAGE_TABLE
-#endif
-
-/*H:320
- * The page table code is curly enough to need helper functions to keep it
- * clear and clean.  The kernel itself provides many of them; one advantage
- * of insisting that the Guest and Host use the same CONFIG_X86_PAE setting.
- *
- * There are two functions which return pointers to the shadow (aka "real")
- * page tables.
- *
- * spgd_addr() takes the virtual address and returns a pointer to the top-level
- * page directory entry (PGD) for that address.  Since we keep track of several
- * page tables, the "i" argument tells us which one we're interested in (it's
- * usually the current one).
- */
-static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
-{
-	unsigned int index = pgd_index(vaddr);
-
-	/* Return a pointer index'th pgd entry for the i'th page table. */
-	return &cpu->lg->pgdirs[i].pgdir[index];
-}
-
-#ifdef CONFIG_X86_PAE
-/*
- * This routine then takes the PGD entry given above, which contains the
- * address of the PMD page.  It then returns a pointer to the PMD entry for the
- * given address.
- */
-static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
-{
-	unsigned int index = pmd_index(vaddr);
-	pmd_t *page;
-
-	/* You should never call this if the PGD entry wasn't valid */
-	BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
-	page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
-
-	return &page[index];
-}
-#endif
-
-/*
- * This routine then takes the page directory entry returned above, which
- * contains the address of the page table entry (PTE) page.  It then returns a
- * pointer to the PTE entry for the given address.
- */
-static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
-{
-#ifdef CONFIG_X86_PAE
-	pmd_t *pmd = spmd_addr(cpu, spgd, vaddr);
-	pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT);
-
-	/* You should never call this if the PMD entry wasn't valid */
-	BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT));
-#else
-	pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
-	/* You should never call this if the PGD entry wasn't valid */
-	BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
-#endif
-
-	return &page[pte_index(vaddr)];
-}
-
-/*
- * These functions are just like the above, except they access the Guest
- * page tables.  Hence they return a Guest address.
- */
-static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
-{
-	unsigned int index = vaddr >> (PGDIR_SHIFT);
-	return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t);
-}
-
-#ifdef CONFIG_X86_PAE
-/* Follow the PGD to the PMD. */
-static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
-{
-	unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
-	BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
-	return gpage + pmd_index(vaddr) * sizeof(pmd_t);
-}
-
-/* Follow the PMD to the PTE. */
-static unsigned long gpte_addr(struct lg_cpu *cpu,
-			       pmd_t gpmd, unsigned long vaddr)
-{
-	unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT;
-
-	BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT));
-	return gpage + pte_index(vaddr) * sizeof(pte_t);
-}
-#else
-/* Follow the PGD to the PTE (no mid-level for !PAE). */
-static unsigned long gpte_addr(struct lg_cpu *cpu,
-				pgd_t gpgd, unsigned long vaddr)
-{
-	unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
-
-	BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
-	return gpage + pte_index(vaddr) * sizeof(pte_t);
-}
-#endif
-/*:*/
-
-/*M:007
- * get_pfn is slow: we could probably try to grab batches of pages here as
- * an optimization (ie. pre-faulting).
-:*/
-
-/*H:350
- * This routine takes a page number given by the Guest and converts it to
- * an actual, physical page number.  It can fail for several reasons: the
- * virtual address might not be mapped by the Launcher, the write flag is set
- * and the page is read-only, or the write flag was set and the page was
- * shared so had to be copied, but we ran out of memory.
- *
- * This holds a reference to the page, so release_pte() is careful to put that
- * back.
- */
-static unsigned long get_pfn(unsigned long virtpfn, int write)
-{
-	struct page *page;
-
-	/* gup me one page at this address please! */
-	if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1)
-		return page_to_pfn(page);
-
-	/* This value indicates failure. */
-	return -1UL;
-}
-
-/*H:340
- * Converting a Guest page table entry to a shadow (ie. real) page table
- * entry can be a little tricky.  The flags are (almost) the same, but the
- * Guest PTE contains a virtual page number: the CPU needs the real page
- * number.
- */
-static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
-{
-	unsigned long pfn, base, flags;
-
-	/*
-	 * The Guest sets the global flag, because it thinks that it is using
-	 * PGE.  We only told it to use PGE so it would tell us whether it was
-	 * flushing a kernel mapping or a userspace mapping.  We don't actually
-	 * use the global bit, so throw it away.
-	 */
-	flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
-
-	/* The Guest's pages are offset inside the Launcher. */
-	base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE;
-
-	/*
-	 * We need a temporary "unsigned long" variable to hold the answer from
-	 * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
-	 * fit in spte.pfn.  get_pfn() finds the real physical number of the
-	 * page, given the virtual number.
-	 */
-	pfn = get_pfn(base + pte_pfn(gpte), write);
-	if (pfn == -1UL) {
-		kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte));
-		/*
-		 * When we destroy the Guest, we'll go through the shadow page
-		 * tables and release_pte() them.  Make sure we don't think
-		 * this one is valid!
-		 */
-		flags = 0;
-	}
-	/* Now we assemble our shadow PTE from the page number and flags. */
-	return pfn_pte(pfn, __pgprot(flags));
-}
-
-/*H:460 And to complete the chain, release_pte() looks like this: */
-static void release_pte(pte_t pte)
-{
-	/*
-	 * Remember that get_user_pages_fast() took a reference to the page, in
-	 * get_pfn()?  We have to put it back now.
-	 */
-	if (pte_flags(pte) & _PAGE_PRESENT)
-		put_page(pte_page(pte));
-}
-/*:*/
-
-static bool gpte_in_iomem(struct lg_cpu *cpu, pte_t gpte)
-{
-	/* We don't handle large pages. */
-	if (pte_flags(gpte) & _PAGE_PSE)
-		return false;
-
-	return (pte_pfn(gpte) >= cpu->lg->pfn_limit
-		&& pte_pfn(gpte) < cpu->lg->device_limit);
-}
-
-static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
-{
-	if ((pte_flags(gpte) & _PAGE_PSE) ||
-	    pte_pfn(gpte) >= cpu->lg->pfn_limit) {
-		kill_guest(cpu, "bad page table entry");
-		return false;
-	}
-	return true;
-}
-
-static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
-{
-	if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
-	    (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) {
-		kill_guest(cpu, "bad page directory entry");
-		return false;
-	}
-	return true;
-}
-
-#ifdef CONFIG_X86_PAE
-static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
-{
-	if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
-	    (pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) {
-		kill_guest(cpu, "bad page middle directory entry");
-		return false;
-	}
-	return true;
-}
-#endif
-
-/*H:331
- * This is the core routine to walk the shadow page tables and find the page
- * table entry for a specific address.
- *
- * If allocate is set, then we allocate any missing levels, setting the flags
- * on the new page directory and mid-level directories using the arguments
- * (which are copied from the Guest's page table entries).
- */
-static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
-			int pgd_flags, int pmd_flags)
-{
-	pgd_t *spgd;
-	/* Mid level for PAE. */
-#ifdef CONFIG_X86_PAE
-	pmd_t *spmd;
-#endif
-
-	/* Get top level entry. */
-	spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
-	if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
-		/* No shadow entry: allocate a new shadow PTE page. */
-		unsigned long ptepage;
-
-		/* If they didn't want us to allocate anything, stop. */
-		if (!allocate)
-			return NULL;
-
-		ptepage = get_zeroed_page(GFP_KERNEL);
-		/*
-		 * This is not really the Guest's fault, but killing it is
-		 * simple for this corner case.
-		 */
-		if (!ptepage) {
-			kill_guest(cpu, "out of memory allocating pte page");
-			return NULL;
-		}
-		/*
-		 * And we copy the flags to the shadow PGD entry.  The page
-		 * number in the shadow PGD is the page we just allocated.
-		 */
-		set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags));
-	}
-
-	/*
-	 * Intel's Physical Address Extension actually uses three levels of
-	 * page tables, so we need to look in the mid-level.
-	 */
-#ifdef CONFIG_X86_PAE
-	/* Now look at the mid-level shadow entry. */
-	spmd = spmd_addr(cpu, *spgd, vaddr);
-
-	if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
-		/* No shadow entry: allocate a new shadow PTE page. */
-		unsigned long ptepage;
-
-		/* If they didn't want us to allocate anything, stop. */
-		if (!allocate)
-			return NULL;
-
-		ptepage = get_zeroed_page(GFP_KERNEL);
-
-		/*
-		 * This is not really the Guest's fault, but killing it is
-		 * simple for this corner case.
-		 */
-		if (!ptepage) {
-			kill_guest(cpu, "out of memory allocating pmd page");
-			return NULL;
-		}
-
-		/*
-		 * And we copy the flags to the shadow PMD entry.  The page
-		 * number in the shadow PMD is the page we just allocated.
-		 */
-		set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags));
-	}
-#endif
-
-	/* Get the pointer to the shadow PTE entry we're going to set. */
-	return spte_addr(cpu, *spgd, vaddr);
-}
-
-/*H:330
- * (i) Looking up a page table entry when the Guest faults.
- *
- * We saw this call in run_guest(): when we see a page fault in the Guest, we
- * come here.  That's because we only set up the shadow page tables lazily as
- * they're needed, so we get page faults all the time and quietly fix them up
- * and return to the Guest without it knowing.
- *
- * If we fixed up the fault (ie. we mapped the address), this routine returns
- * true.  Otherwise, it was a real fault and we need to tell the Guest.
- *
- * There's a corner case: they're trying to access memory between
- * pfn_limit and device_limit, which is I/O memory.  In this case, we
- * return false and set @iomem to the physical address, so the the
- * Launcher can handle the instruction manually.
- */
-bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode,
-		 unsigned long *iomem)
-{
-	unsigned long gpte_ptr;
-	pte_t gpte;
-	pte_t *spte;
-	pmd_t gpmd;
-	pgd_t gpgd;
-
-	*iomem = 0;
-
-	/* We never demand page the Switcher, so trying is a mistake. */
-	if (vaddr >= switcher_addr)
-		return false;
-
-	/* First step: get the top-level Guest page table entry. */
-	if (unlikely(cpu->linear_pages)) {
-		/* Faking up a linear mapping. */
-		gpgd = __pgd(CHECK_GPGD_MASK);
-	} else {
-		gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
-		/* Toplevel not present?  We can't map it in. */
-		if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
-			return false;
-
-		/* 
-		 * This kills the Guest if it has weird flags or tries to
-		 * refer to a "physical" address outside the bounds.
-		 */
-		if (!check_gpgd(cpu, gpgd))
-			return false;
-	}
-
-	/* This "mid-level" entry is only used for non-linear, PAE mode. */
-	gpmd = __pmd(_PAGE_TABLE);
-
-#ifdef CONFIG_X86_PAE
-	if (likely(!cpu->linear_pages)) {
-		gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
-		/* Middle level not present?  We can't map it in. */
-		if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
-			return false;
-
-		/* 
-		 * This kills the Guest if it has weird flags or tries to
-		 * refer to a "physical" address outside the bounds.
-		 */
-		if (!check_gpmd(cpu, gpmd))
-			return false;
-	}
-
-	/*
-	 * OK, now we look at the lower level in the Guest page table: keep its
-	 * address, because we might update it later.
-	 */
-	gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
-#else
-	/*
-	 * OK, now we look at the lower level in the Guest page table: keep its
-	 * address, because we might update it later.
-	 */
-	gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
-#endif
-
-	if (unlikely(cpu->linear_pages)) {
-		/* Linear?  Make up a PTE which points to same page. */
-		gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
-	} else {
-		/* Read the actual PTE value. */
-		gpte = lgread(cpu, gpte_ptr, pte_t);
-	}
-
-	/* If this page isn't in the Guest page tables, we can't page it in. */
-	if (!(pte_flags(gpte) & _PAGE_PRESENT))
-		return false;
-
-	/*
-	 * Check they're not trying to write to a page the Guest wants
-	 * read-only (bit 2 of errcode == write).
-	 */
-	if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
-		return false;
-
-	/* User access to a kernel-only page? (bit 3 == user access) */
-	if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
-		return false;
-
-	/* If they're accessing io memory, we expect a fault. */
-	if (gpte_in_iomem(cpu, gpte)) {
-		*iomem = (pte_pfn(gpte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK);
-		return false;
-	}
-
-	/*
-	 * Check that the Guest PTE flags are OK, and the page number is below
-	 * the pfn_limit (ie. not mapping the Launcher binary).
-	 */
-	if (!check_gpte(cpu, gpte))
-		return false;
-
-	/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
-	gpte = pte_mkyoung(gpte);
-	if (errcode & 2)
-		gpte = pte_mkdirty(gpte);
-
-	/* Get the pointer to the shadow PTE entry we're going to set. */
-	spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
-	if (!spte)
-		return false;
-
-	/*
-	 * If there was a valid shadow PTE entry here before, we release it.
-	 * This can happen with a write to a previously read-only entry.
-	 */
-	release_pte(*spte);
-
-	/*
-	 * If this is a write, we insist that the Guest page is writable (the
-	 * final arg to gpte_to_spte()).
-	 */
-	if (pte_dirty(gpte))
-		*spte = gpte_to_spte(cpu, gpte, 1);
-	else
-		/*
-		 * If this is a read, don't set the "writable" bit in the page
-		 * table entry, even if the Guest says it's writable.  That way
-		 * we will come back here when a write does actually occur, so
-		 * we can update the Guest's _PAGE_DIRTY flag.
-		 */
-		set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
-
-	/*
-	 * Finally, we write the Guest PTE entry back: we've set the
-	 * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
-	 */
-	if (likely(!cpu->linear_pages))
-		lgwrite(cpu, gpte_ptr, pte_t, gpte);
-
-	/*
-	 * The fault is fixed, the page table is populated, the mapping
-	 * manipulated, the result returned and the code complete.  A small
-	 * delay and a trace of alliteration are the only indications the Guest
-	 * has that a page fault occurred at all.
-	 */
-	return true;
-}
-
-/*H:360
- * (ii) Making sure the Guest stack is mapped.
- *
- * Remember that direct traps into the Guest need a mapped Guest kernel stack.
- * pin_stack_pages() calls us here: we could simply call demand_page(), but as
- * we've seen that logic is quite long, and usually the stack pages are already
- * mapped, so it's overkill.
- *
- * This is a quick version which answers the question: is this virtual address
- * mapped by the shadow page tables, and is it writable?
- */
-static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
-{
-	pte_t *spte;
-	unsigned long flags;
-
-	/* You can't put your stack in the Switcher! */
-	if (vaddr >= switcher_addr)
-		return false;
-
-	/* If there's no shadow PTE, it's not writable. */
-	spte = find_spte(cpu, vaddr, false, 0, 0);
-	if (!spte)
-		return false;
-
-	/*
-	 * Check the flags on the pte entry itself: it must be present and
-	 * writable.
-	 */
-	flags = pte_flags(*spte);
-	return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
-}
-
-/*
- * So, when pin_stack_pages() asks us to pin a page, we check if it's already
- * in the page tables, and if not, we call demand_page() with error code 2
- * (meaning "write").
- */
-void pin_page(struct lg_cpu *cpu, unsigned long vaddr)
-{
-	unsigned long iomem;
-
-	if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2, &iomem))
-		kill_guest(cpu, "bad stack page %#lx", vaddr);
-}
-/*:*/
-
-#ifdef CONFIG_X86_PAE
-static void release_pmd(pmd_t *spmd)
-{
-	/* If the entry's not present, there's nothing to release. */
-	if (pmd_flags(*spmd) & _PAGE_PRESENT) {
-		unsigned int i;
-		pte_t *ptepage = __va(pmd_pfn(*spmd) << PAGE_SHIFT);
-		/* For each entry in the page, we might need to release it. */
-		for (i = 0; i < PTRS_PER_PTE; i++)
-			release_pte(ptepage[i]);
-		/* Now we can free the page of PTEs */
-		free_page((long)ptepage);
-		/* And zero out the PMD entry so we never release it twice. */
-		set_pmd(spmd, __pmd(0));
-	}
-}
-
-static void release_pgd(pgd_t *spgd)
-{
-	/* If the entry's not present, there's nothing to release. */
-	if (pgd_flags(*spgd) & _PAGE_PRESENT) {
-		unsigned int i;
-		pmd_t *pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
-
-		for (i = 0; i < PTRS_PER_PMD; i++)
-			release_pmd(&pmdpage[i]);
-
-		/* Now we can free the page of PMDs */
-		free_page((long)pmdpage);
-		/* And zero out the PGD entry so we never release it twice. */
-		set_pgd(spgd, __pgd(0));
-	}
-}
-
-#else /* !CONFIG_X86_PAE */
-/*H:450
- * If we chase down the release_pgd() code, the non-PAE version looks like
- * this.  The PAE version is almost identical, but instead of calling
- * release_pte it calls release_pmd(), which looks much like this.
- */
-static void release_pgd(pgd_t *spgd)
-{
-	/* If the entry's not present, there's nothing to release. */
-	if (pgd_flags(*spgd) & _PAGE_PRESENT) {
-		unsigned int i;
-		/*
-		 * Converting the pfn to find the actual PTE page is easy: turn
-		 * the page number into a physical address, then convert to a
-		 * virtual address (easy for kernel pages like this one).
-		 */
-		pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
-		/* For each entry in the page, we might need to release it. */
-		for (i = 0; i < PTRS_PER_PTE; i++)
-			release_pte(ptepage[i]);
-		/* Now we can free the page of PTEs */
-		free_page((long)ptepage);
-		/* And zero out the PGD entry so we never release it twice. */
-		*spgd = __pgd(0);
-	}
-}
-#endif
-
-/*H:445
- * We saw flush_user_mappings() twice: once from the flush_user_mappings()
- * hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
- * It simply releases every PTE page from 0 up to the Guest's kernel address.
- */
-static void flush_user_mappings(struct lguest *lg, int idx)
-{
-	unsigned int i;
-	/* Release every pgd entry up to the kernel's address. */
-	for (i = 0; i < pgd_index(lg->kernel_address); i++)
-		release_pgd(lg->pgdirs[idx].pgdir + i);
-}
-
-/*H:440
- * (v) Flushing (throwing away) page tables,
- *
- * The Guest has a hypercall to throw away the page tables: it's used when a
- * large number of mappings have been changed.
- */
-void guest_pagetable_flush_user(struct lg_cpu *cpu)
-{
-	/* Drop the userspace part of the current page table. */
-	flush_user_mappings(cpu->lg, cpu->cpu_pgd);
-}
-/*:*/
-
-/* We walk down the guest page tables to get a guest-physical address */
-bool __guest_pa(struct lg_cpu *cpu, unsigned long vaddr, unsigned long *paddr)
-{
-	pgd_t gpgd;
-	pte_t gpte;
-#ifdef CONFIG_X86_PAE
-	pmd_t gpmd;
-#endif
-
-	/* Still not set up?  Just map 1:1. */
-	if (unlikely(cpu->linear_pages)) {
-		*paddr = vaddr;
-		return true;
-	}
-
-	/* First step: get the top-level Guest page table entry. */
-	gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
-	/* Toplevel not present?  We can't map it in. */
-	if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
-		goto fail;
-
-#ifdef CONFIG_X86_PAE
-	gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
-	if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
-		goto fail;
-	gpte = lgread(cpu, gpte_addr(cpu, gpmd, vaddr), pte_t);
-#else
-	gpte = lgread(cpu, gpte_addr(cpu, gpgd, vaddr), pte_t);
-#endif
-	if (!(pte_flags(gpte) & _PAGE_PRESENT))
-		goto fail;
-
-	*paddr = pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
-	return true;
-
-fail:
-	*paddr = -1UL;
-	return false;
-}
-
-/*
- * This is the version we normally use: kills the Guest if it uses a
- * bad address
- */
-unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
-{
-	unsigned long paddr;
-
-	if (!__guest_pa(cpu, vaddr, &paddr))
-		kill_guest(cpu, "Bad address %#lx", vaddr);
-	return paddr;
-}
-
-/*
- * We keep several page tables.  This is a simple routine to find the page
- * table (if any) corresponding to this top-level address the Guest has given
- * us.
- */
-static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
-{
-	unsigned int i;
-	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
-		if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable)
-			break;
-	return i;
-}
-
-/*H:435
- * And this is us, creating the new page directory.  If we really do
- * allocate a new one (and so the kernel parts are not there), we set
- * blank_pgdir.
- */
-static unsigned int new_pgdir(struct lg_cpu *cpu,
-			      unsigned long gpgdir,
-			      int *blank_pgdir)
-{
-	unsigned int next;
-
-	/*
-	 * We pick one entry at random to throw out.  Choosing the Least
-	 * Recently Used might be better, but this is easy.
-	 */
-	next = prandom_u32() % ARRAY_SIZE(cpu->lg->pgdirs);
-	/* If it's never been allocated at all before, try now. */
-	if (!cpu->lg->pgdirs[next].pgdir) {
-		cpu->lg->pgdirs[next].pgdir =
-					(pgd_t *)get_zeroed_page(GFP_KERNEL);
-		/* If the allocation fails, just keep using the one we have */
-		if (!cpu->lg->pgdirs[next].pgdir)
-			next = cpu->cpu_pgd;
-		else {
-			/*
-			 * This is a blank page, so there are no kernel
-			 * mappings: caller must map the stack!
-			 */
-			*blank_pgdir = 1;
-		}
-	}
-	/* Record which Guest toplevel this shadows. */
-	cpu->lg->pgdirs[next].gpgdir = gpgdir;
-	/* Release all the non-kernel mappings. */
-	flush_user_mappings(cpu->lg, next);
-
-	/* This hasn't run on any CPU at all. */
-	cpu->lg->pgdirs[next].last_host_cpu = -1;
-
-	return next;
-}
-
-/*H:501
- * We do need the Switcher code mapped at all times, so we allocate that
- * part of the Guest page table here.  We map the Switcher code immediately,
- * but defer mapping of the guest register page and IDT/LDT etc page until
- * just before we run the guest in map_switcher_in_guest().
- *
- * We *could* do this setup in map_switcher_in_guest(), but at that point
- * we've interrupts disabled, and allocating pages like that is fraught: we
- * can't sleep if we need to free up some memory.
- */
-static bool allocate_switcher_mapping(struct lg_cpu *cpu)
-{
-	int i;
-
-	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
-		pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
-				       CHECK_GPGD_MASK, _PAGE_TABLE);
-		if (!pte)
-			return false;
-
-		/*
-		 * Map the switcher page if not already there.  It might
-		 * already be there because we call allocate_switcher_mapping()
-		 * in guest_set_pgd() just in case it did discard our Switcher
-		 * mapping, but it probably didn't.
-		 */
-		if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {
-			/* Get a reference to the Switcher page. */
-			get_page(lg_switcher_pages[0]);
-			/* Create a read-only, exectuable, kernel-style PTE */
-			set_pte(pte,
-				mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
-		}
-	}
-	cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;
-	return true;
-}
-
-/*H:470
- * Finally, a routine which throws away everything: all PGD entries in all
- * the shadow page tables, including the Guest's kernel mappings.  This is used
- * when we destroy the Guest.
- */
-static void release_all_pagetables(struct lguest *lg)
-{
-	unsigned int i, j;
-
-	/* Every shadow pagetable this Guest has */
-	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) {
-		if (!lg->pgdirs[i].pgdir)
-			continue;
-
-		/* Every PGD entry. */
-		for (j = 0; j < PTRS_PER_PGD; j++)
-			release_pgd(lg->pgdirs[i].pgdir + j);
-		lg->pgdirs[i].switcher_mapped = false;
-		lg->pgdirs[i].last_host_cpu = -1;
-	}
-}
-
-/*
- * We also throw away everything when a Guest tells us it's changed a kernel
- * mapping.  Since kernel mappings are in every page table, it's easiest to
- * throw them all away.  This traps the Guest in amber for a while as
- * everything faults back in, but it's rare.
- */
-void guest_pagetable_clear_all(struct lg_cpu *cpu)
-{
-	release_all_pagetables(cpu->lg);
-	/* We need the Guest kernel stack mapped again. */
-	pin_stack_pages(cpu);
-	/* And we need Switcher allocated. */
-	if (!allocate_switcher_mapping(cpu))
-		kill_guest(cpu, "Cannot populate switcher mapping");
-}
-
-/*H:430
- * (iv) Switching page tables
- *
- * Now we've seen all the page table setting and manipulation, let's see
- * what happens when the Guest changes page tables (ie. changes the top-level
- * pgdir).  This occurs on almost every context switch.
- */
-void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
-{
-	int newpgdir, repin = 0;
-
-	/*
-	 * The very first time they call this, we're actually running without
-	 * any page tables; we've been making it up.  Throw them away now.
-	 */
-	if (unlikely(cpu->linear_pages)) {
-		release_all_pagetables(cpu->lg);
-		cpu->linear_pages = false;
-		/* Force allocation of a new pgdir. */
-		newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
-	} else {
-		/* Look to see if we have this one already. */
-		newpgdir = find_pgdir(cpu->lg, pgtable);
-	}
-
-	/*
-	 * If not, we allocate or mug an existing one: if it's a fresh one,
-	 * repin gets set to 1.
-	 */
-	if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
-		newpgdir = new_pgdir(cpu, pgtable, &repin);
-	/* Change the current pgd index to the new one. */
-	cpu->cpu_pgd = newpgdir;
-	/*
-	 * If it was completely blank, we map in the Guest kernel stack and
-	 * the Switcher.
-	 */
-	if (repin)
-		pin_stack_pages(cpu);
-
-	if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {
-		if (!allocate_switcher_mapping(cpu))
-			kill_guest(cpu, "Cannot populate switcher mapping");
-	}
-}
-/*:*/
-
-/*M:009
- * Since we throw away all mappings when a kernel mapping changes, our
- * performance sucks for guests using highmem.  In fact, a guest with
- * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
- * usually slower than a Guest with less memory.
- *
- * This, of course, cannot be fixed.  It would take some kind of... well, I
- * don't know, but the term "puissant code-fu" comes to mind.
-:*/
-
-/*H:420
- * This is the routine which actually sets the page table entry for then
- * "idx"'th shadow page table.
- *
- * Normally, we can just throw out the old entry and replace it with 0: if they
- * use it demand_page() will put the new entry in.  We need to do this anyway:
- * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
- * is read from, and _PAGE_DIRTY when it's written to.
- *
- * But Avi Kivity pointed out that most Operating Systems (Linux included) set
- * these bits on PTEs immediately anyway.  This is done to save the CPU from
- * having to update them, but it helps us the same way: if they set
- * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
- * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
- */
-static void __guest_set_pte(struct lg_cpu *cpu, int idx,
-		       unsigned long vaddr, pte_t gpte)
-{
-	/* Look up the matching shadow page directory entry. */
-	pgd_t *spgd = spgd_addr(cpu, idx, vaddr);
-#ifdef CONFIG_X86_PAE
-	pmd_t *spmd;
-#endif
-
-	/* If the top level isn't present, there's no entry to update. */
-	if (pgd_flags(*spgd) & _PAGE_PRESENT) {
-#ifdef CONFIG_X86_PAE
-		spmd = spmd_addr(cpu, *spgd, vaddr);
-		if (pmd_flags(*spmd) & _PAGE_PRESENT) {
-#endif
-			/* Otherwise, start by releasing the existing entry. */
-			pte_t *spte = spte_addr(cpu, *spgd, vaddr);
-			release_pte(*spte);
-
-			/*
-			 * If they're setting this entry as dirty or accessed,
-			 * we might as well put that entry they've given us in
-			 * now.  This shaves 10% off a copy-on-write
-			 * micro-benchmark.
-			 */
-			if ((pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED))
-			    && !gpte_in_iomem(cpu, gpte)) {
-				if (!check_gpte(cpu, gpte))
-					return;
-				set_pte(spte,
-					gpte_to_spte(cpu, gpte,
-						pte_flags(gpte) & _PAGE_DIRTY));
-			} else {
-				/*
-				 * Otherwise kill it and we can demand_page()
-				 * it in later.
-				 */
-				set_pte(spte, __pte(0));
-			}
-#ifdef CONFIG_X86_PAE
-		}
-#endif
-	}
-}
-
-/*H:410
- * Updating a PTE entry is a little trickier.
- *
- * We keep track of several different page tables (the Guest uses one for each
- * process, so it makes sense to cache at least a few).  Each of these have
- * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
- * all processes.  So when the page table above that address changes, we update
- * all the page tables, not just the current one.  This is rare.
- *
- * The benefit is that when we have to track a new page table, we can keep all
- * the kernel mappings.  This speeds up context switch immensely.
- */
-void guest_set_pte(struct lg_cpu *cpu,
-		   unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
-{
-	/* We don't let you remap the Switcher; we need it to get back! */
-	if (vaddr >= switcher_addr) {
-		kill_guest(cpu, "attempt to set pte into Switcher pages");
-		return;
-	}
-
-	/*
-	 * Kernel mappings must be changed on all top levels.  Slow, but doesn't
-	 * happen often.
-	 */
-	if (vaddr >= cpu->lg->kernel_address) {
-		unsigned int i;
-		for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
-			if (cpu->lg->pgdirs[i].pgdir)
-				__guest_set_pte(cpu, i, vaddr, gpte);
-	} else {
-		/* Is this page table one we have a shadow for? */
-		int pgdir = find_pgdir(cpu->lg, gpgdir);
-		if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
-			/* If so, do the update. */
-			__guest_set_pte(cpu, pgdir, vaddr, gpte);
-	}
-}
-
-/*H:400
- * (iii) Setting up a page table entry when the Guest tells us one has changed.
- *
- * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
- * with the other side of page tables while we're here: what happens when the
- * Guest asks for a page table to be updated?
- *
- * We already saw that demand_page() will fill in the shadow page tables when
- * needed, so we can simply remove shadow page table entries whenever the Guest
- * tells us they've changed.  When the Guest tries to use the new entry it will
- * fault and demand_page() will fix it up.
- *
- * So with that in mind here's our code to update a (top-level) PGD entry:
- */
-void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
-{
-	int pgdir;
-
-	if (idx > PTRS_PER_PGD) {
-		kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
-			   idx, PTRS_PER_PGD);
-		return;
-	}
-
-	/* If they're talking about a page table we have a shadow for... */
-	pgdir = find_pgdir(lg, gpgdir);
-	if (pgdir < ARRAY_SIZE(lg->pgdirs)) {
-		/* ... throw it away. */
-		release_pgd(lg->pgdirs[pgdir].pgdir + idx);
-		/* That might have been the Switcher mapping, remap it. */
-		if (!allocate_switcher_mapping(&lg->cpus[0])) {
-			kill_guest(&lg->cpus[0],
-				   "Cannot populate switcher mapping");
-		}
-		lg->pgdirs[pgdir].last_host_cpu = -1;
-	}
-}
-
-#ifdef CONFIG_X86_PAE
-/* For setting a mid-level, we just throw everything away.  It's easy. */
-void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
-{
-	guest_pagetable_c